The Optical–infrared Extinction Curve and Its Variation in the Milky Way

Schlafly, Edward F.; Meisner, Aaron M.; Stutz, Amelia M.; Kainulainen, J.; Peek, J. E. G.; Tchernyshyov, Kirill; Rix, H. W.; Finkbeiner, Douglas P.; Covey, Kevin R.; Green, Gregory; Bell, Eric F.; Burgett, W. S.; Chambers, K.; Draper, P. W.; Flewelling, H.; Hodapp, Klaus W.; Kaiser, N.; Magnier, E. A.; Martin, N. F.; Metcalfe, N.; Wainscoat, R. J.; Waters, C.

doi:10.3847/0004-637x/821/2/78

Cited by 249 publications

(312 citation statements)

References 76 publications

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“…The joint comparison of dust emission and extinction data to other gas tracers will provide additional information on the relation between the total gas and dust, including the abundant dark neutral medium, and will help to better constrain the evolution of dust properties, in particular with regard to potential variations of the extinction curve (Schlafly et al 2016).…”

Section: Discussionmentioning

confidence: 99%

Cosmic rays, gas and dust in nearby anticentre clouds

Remy

Grenier

Marshall

et al. 2017

A&A

187

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Aims. We aim to explore the capabilities of dust emission and γ rays for probing the properties of the interstellar medium in the nearby anti-centre region, using γ-ray observations with the Fermi Large Area Telescope (LAT), and the thermal dust optical depth inferred from Planck and IRAS observations. We also aim to study massive star-forming clouds including the well known Taurus, Auriga, Perseus, and California molecular clouds, as well as a more diffuse structure which we refer to as Cetus. In particular, we aim at quantifying potential variations in cosmic-ray density and dust properties per gas nucleon across the different gas phases and different clouds, and at measuring the CO-to-H 2 conversion factor, X CO , in different environments. Methods. We have separated six nearby anti-centre clouds that are coherent in velocities and distances, from the Galactic-disc background in H i 21-cm and 12 CO 2.6-mm line emission. We have jointly modelled the γ-ray intensity recorded between 0.4 and 100 GeV, and the dust optical depth τ 353 at 353 GHz as a combination of H i -bright, CO-bright, and ionised gas components. The complementary information from dust emission and γ rays was used to reveal the gas not seen, or poorly traced, by H i , free-free, and 12 CO emissions, namely (i) the opaque H i and diffuse H 2 present in the Dark Neutral Medium at the atomic-molecular transition, and (ii) the dense H 2 to be added where 12 CO lines saturate. Results. The measured interstellar γ-ray spectra support a uniform penetration of the cosmic rays with energies above a few GeV through the clouds, from the atomic envelopes to the 12 CO-bright cores, and with a small ±9% cloud-to-cloud dispersion in particle flux. We detect the ionised gas from the H ii region NGC1499 in the dust and γ-ray emissions and measure its mean electron density and temperature. We find a gradual increase in grain opacity as the gas (atomic or molecular) becomes more dense. The increase reaches a factor of four to six in the cold molecular regions that are well shielded from stellar radiation. Consequently, the X CO factor derived from dust is systematically larger by 30% to 130% than the γ-ray estimate. We also evaluate the average γ-ray X CO factor for each cloud, and find that X CO tends to decrease from diffuse to more compact molecular clouds, as expected from theory. We find X CO factors in the anti-centre clouds close to or below 10 20 cm −2 K −1 km −1 s, in agreement with other estimates in the solar neighbourhood. Together, they confirm the long-standing unexplained discrepancy, by a factor of two, between the mean X CO values measured at parsec scales in nearby clouds and those obtained at kiloparsec scale in the Galaxy. Our results also highlight large quantitative discrepancies in 12 CO intensities between simulations and observations at low molecular gas densities.

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Section: Discussionmentioning

confidence: 99%

Cosmic rays, gas and dust in nearby anticentre clouds

Remy

Grenier

Marshall

et al. 2017

A&A

187

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“…Using E(B-V) to infer N H relies on the assumption that local environment does not change dramatically from sightline to sightline. This is reasonable as the gas-to-dust ratio is relatively constant over a galaxy's disk (Sandstrom et al 2013) and the dust extinction curve only weakly varies across kpc scales (Schlafly et al 2016). Since the metal content of M33's ISM is not yet Table 3.…”

Section: Hydrogen Column Density In Front Of the Starsmentioning

confidence: 95%

HST/Cos Observations of Ionized Gas Accretion at the Disk–halo Interface of M33

Zheng

Peek

Werk

et al. 2017

ApJ

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We report the detection of accreting ionized gas at the disk-halo interface of the nearby galaxy M33. We analyze HST/COS absorption-line spectra of seven ultraviolet-bright stars evenly distributed across the disk of M33. We find Si IV absorption components consistently redshifted relative to the bulk M33's ISM absorption along all the sightlines. The Si IV detection indicates an enriched, diskwide, ionized gas inflow toward the disk. This inflow is most likely multi-phase as the redshifted components can also be observed in ions with lower ionization states (e.g., S II, P II, Fe II, Si II). Kinematic modeling of the inflow is consistent with an accreting layer at the disk-halo interface of M33, which has an accretion velocity of 110 +15 −20 km s −1 at a distance of 1.5+1.0 −1.0 kiloparsec above the disk. The modeling indicates a total mass of ∼ 3.9 × 10 7 M for the accreting material at the diskhalo interface on the near side of the M33 disk , with an accretion rate of ∼ 2.9 M yr −1 . The high accretion rate and the level of metal-enrichment suggest the inflow is likely to be the fall back of M33 gas from a galactic fountain and/or the gas pulled loosed during a close interaction between M31 and M33. Our study of M33 is the first to unambiguously reveal the existence of a disk-wide, ionized gas inflow beyond the Milky Way, providing a better understanding of gas accretion in the vicinity of a galaxy disk.

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“…Outside this layer they are anticorrelated: at high and medium latitudes, less reddening corresponds to larger R V . In an extensive study of the absorption law near the galactic plane, Schlafly, et al (2016), have found a strong correlation between R V and emission in the far IR. This can be explained if the absorption law depends primarily on the size of the dust particles.…”

Section: Three-dimensional Maps Of Extinctionmentioning

confidence: 99%

“…The data of Davenport, et al (2014), are material for further more detailed analysis. Schlafly, et al (2016), have pointed out that in many studies that claim to examine largescale variations in the extinction law at high latitudes, a single narrow range of wavelengths and/or a small number of OB stars have been used, which naturally lie within a narrow layer near the galactic plane; thus, only a few properties of specific stars and media in a negligibly small part of the Galaxy have been analyzed. One example is a much cited (more than 70 times) paper of Fitzpatrick and Massa (2009) that analyzed only 14 OB stars within |Z| < 100 pc.…”

Section: Variations In the Extinction Lawmentioning

confidence: 99%

Interstellar Extinction

Gontcharov

2016

Astrophysics

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Key words: interstellar extinction: reddening: interstellar dust particles: characteristics and properties of the Milky Way galaxy.This review describes our current understanding of interstellar extinction. This differ substantially from the ideas of the 20th century. With infrared surveys of hundreds of millions of stars over the entire sky, such as 2MASS, SPITZER-IRAC, and WISE, we have looked at the densest and most rarefied regions of the interstellar medium at distances of a few kpc from the sun. Observations at infrared and microwave wavelengths, where the bulk of the interstellar dust absorbs and radiates, have brought us closer to an understanding of the distribution of the dust particles on scales of the Galaxy and the Universe. We are in the midst of a scientific revolution in our understanding of the interstellar medium and dust. Progress in, and the key results of, this revolution are still difficult to predict. Nevertheless, (a) a physically justified model has been developed for the spatial distribution of absorbing material over the nearest few kiloparsecs, including the Gould belt as a dust container, which gives an accurate estimate of the extinction for any object just in terms of its galactic coordinates. It is also clear that (b) the interstellar medium makes up roughly half the mass of matter in the galactic vicinity of the solar system (the other half is made up of stars, their remnants, and dark matter) and (c) the interstellar medium and, especially, dust, differ substantially in different regions of space, and deep space cannot be understood by only studying nearby space. *

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The Optical–infrared Extinction Curve and Its Variation in the Milky Way

Cited by 249 publications

References 76 publications

Cosmic rays, gas and dust in nearby anticentre clouds

Cosmic rays, gas and dust in nearby anticentre clouds

HST/Cos Observations of Ionized Gas Accretion at the Disk–halo Interface of M33

Interstellar Extinction

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